DE2922748A1 - TEST MEANS AND METHOD FOR DETERMINING THE UREA CONTENT IN LIQUIDS - Google Patents

Description

HOFFMANN · ΕΙΤΙ, Ε 6c PAITTNER ^:

DR. ING. E. HOFFMANN (1930-1976). DIPL.-ING. W.EITLE DR. RER. NAT. K. HOFFMANN · Dl PL..ING. W. LEH N

DIPL. -ING. K. FOCHSLE DR. RER. NAT. B. HANSEN ARABELLASTRASSE 4 (STERNHAUS) D-8000 MONCH EN 81 TELEPHONE (089) 911087. TELEX 05-29619 (PATH E)

32, 167 m / wa

MILES LABORATORIES, INC., ELKHART, INDIANA / USA

Test agent and method for determining the urea content in liquids

The invention relates to the determination of the urea content of liquids and aqueous solutions and in particular to test means and methods for stability to improve the colorimetric tests for fast and accurate urea determination.

Urea is one of the essential end products of protein metabolism in the human body. As a result, there

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the concentration of urea in the blood is an indication of kidney function. An increase in the urea concentration in the blood indicates insufficient kidney function. Because toxic substances in the blood in about the same proportion retained at urea level means a high level of non-protein nitrogen or Blood urea nitrogen is a serious matter for the doctor.

One of the most common causes of high blood urea levels (uremia) is kidney disease, which is either acute or chronic. Any inflammation, degenerative, congenital or neoplastic Kidney disease can lead to uremia. The degree of uremia gives a rough index of how the present condition is serious.

In practice, the urea concentration in the blood usually expressed in the form of blood urea nitrogen (BUN). This BUN value represents that present as urea Amount of nitrogen and is approximately half the total urea value. If either the urea or nitrogen value has been determined, so can the other Value can be calculated from the same.

The normal range of BUN values for individuals is between 5 and 20 mg%. The lower values therefore no importance is attached. However, an increase in the BUN values generally indicates the presence an abnormal condition. The most common cause of an increase in blood urea nitrogen is inadequate Excretion, which usually occurs on a

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Kidney disease or urinary obstruction. For example, in acute nephritis, the BUN values between 25 mg% up to 160 mg%. An increased Urea retention also occurs with extensive parenchymal destruction of kidney tissue, as in pyelonephritis, more advanced Nephrosclerosis, renal tuberculosis, cortical renal necrosis, renal malignancy, or kidney dilatation chronic gout. Although the BUN values can go up to 400 mg%, they generally exceed them not 200 mg%.

There is a need in the medical field today for a quick and accurate method of determining the BUN value. In the past, lengthy and time consuming wet chemical processes have been performed to remove these Analysis. Other methods have also been used, such as conductivity measurements, spectrophotometric Methods and colorimetric procedures. While these methods are generally accurate, they are corresponding procedures are very time-consuming and require careful evaluation.

Probably the most frequently used method for determining urea In biological fluids, the urea with the help of the enzyme urease in the presence of a Buffer solution hydrolyzed to ammonium carbonate. The amount of ammonia released is determined colorimetrically. These first method is very specific and sensitive, but has the disadvantage of urease inhibition and inactivation, the problem of reagent stability, as well as the further disadvantage that this method is also endogenous

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Ammonia is determined. Another method is used also hydrolyzed with urease, but a special device is required which is not always available in a routine laboratory. After another The method uses the direct colorimetric reaction of urea in a protein-free film with an organic reagent such as diacetyl monoxime. However, the diacetyl reaction has the disadvantage that the color formed is unstable, as well as the fact that the colors are developed at around 95 ° C and that the volatile Diacetyl has a smell that at least some people find unpleasant.

U.S. Patent 4,074,972 issued to American Monitor Corp. uses a Liquid determination method for urea disclosed based on a reaction between a sample of a biological Liquid and an acidic reagent solution of o-phthalaldehyde and 8- (4-amino-1-methyl-butyl-amino) -6-methoxyquinoline. In this publication neither the teaching nor an indication is given that the reagent solution should be incorporated into a test medium, such as a carrier matrix, or to build in; likewise, no suggestion is made that one loaded with a strong cation exchange resin To use carrier matrix, which is present in its acid form. In addition, this patent specification does not disclose a method solve the stability problem that arises when reagents are combined with the acidic reagent solution. Another problem with the disclosed detection method according to the document is the fact that the Determinations must be carried out at wavelengths in the range from 470 to 540 nm, which is in the vicinity of the Color absorption maximum of the blank is, whereby the

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There is a likelihood that errors will occur in the spectroscopic reflection measurement.

In the industrial field, urea is an important additive for process fluids such as plating or electroplating baths, so that a quick detection means for determining the contained therein Urea concentration is important. Urea itself is used as a fertilizer and it is important a quick means of detection to examine this material for control measures in its production and use at hand.

As a result, there is both medical and the need for a method of determining the urea content of liquids for industrial applications, which quickly and without highly specialized equipment or trained personnel to operate the same can be carried out.

The object of the present invention is to provide a method and a test means for detecting urea and a To provide a method for producing the test agent mentioned, with which the disadvantages of the previously known detection methods and test means are overcome.

The above object is achieved according to the invention by that a test agent for determining the urea content of liquids is made available, which is characterized in that it comprises a carrier matrix loaded with a strong cation exchange resin,

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which is in the acid form, these separately from one another the reagent o-phthalaldehyde and a reagent from the group 3-hydroxy-1,2,3,4-tetrahydrobenz ^ h / quinoline, 3-acetoxy-1,2,3,4-tetrahydrobenz ^ h / quinoline and their Contains incorporated dihydrochloride salts.

With the aid of the test agent according to the invention, the stability the reagents used to prepare the same guaranteed. In addition, influences are due the serum turbidity and the presence of bilirubin when determining the urea content in the blood serum reduced to a minimum.

The test agents according to the invention have a high specificity and sensitivity for the determination of urea in Liquids over a wide range of concentrations.

According to the invention, a colorimetric test agent made available, with which the detection of urea is possible even if the to be examined The amount of liquid is limited. According to the invention, a BUN determination method is made available, which can be done quickly and without the need for highly specialized equipment.

According to the present invention, the test means comprises for the detection or for the determination of the in a test liquid present urea an acid-modified carrier element, which the separate reagents contains. One reagent is o-phthalaldehyde, the other is 3-hydroxy-1,2,3,4-tetrahydrobenzo ^ h / quinoline,

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3-acetoxy-1 _/ 2,3-tetrahydrobenzo 4 _r ^ h7chinolin or their dihydrochloride salts. It is preferred that the reagents are separated by means of a polymeric material from each other.

The test agent is applied by immersing it in a test sample for a moment or a short time or by otherwise applying the test sample to the support matrix and the occurrence of a possible Color change is observed or evaluated.

In the context of this description, the term "liquids" means body fluids such as blood serum, blood plasma, Urine, spinal fluid and also aqueous solutions that contain urea. Although the most preferred application of the test agent and the method according to the invention to body fluids such as In relation to blood serum, it goes without saying that the test agent and the method also apply to industrial liquids can be applied.

According to the invention, there is a single reagent strip produced by the said reagents in a carrier matrix, which in a suitable manner in or on the same, e.g. separated by a polymeric separating layer or barrier. The term "carrier matrix" refers to absorbent and non-absorbent matrices which are in water or other physiological fluids are insoluble and retain their structural integrity in said liquids. Suitable absorbent Matrices include paper, cellulose, wood, synthetic resinous nonwovens, woven and nonwoven fabrics, and the like.

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Non-absorbent matrices include fiberglass and organoplastic materials such as polypropylene and the like. The matrix can advantageously be applied to an insoluble carrier element, such as an organoplastic strip, e.g. polystyrene, by suitable means, such as double-sided adhesive tape, for easier handling be attached or applied.

The reagents incorporated in the carrier matrix react with urea under acidic conditions, whereby they a Chromogen, which forms light above about 550 nm and normally absorb between about 550 and about 700 nm. The quantitative evaluation is carried out by determining or Record the change in reflection at approx. 620 nm Application or contact with the sample.

To determine the desired acidity for the conditions To obtain, it has been shown that it is necessary to modify the carrier matrix with an acidic material or to impregnate. One method for producing the acid-modified carrier matrix comprises impregnation the carrier matrix with acidic substances such as benzenesulfonic acid, benzenesulfonic acid, polystyrene sulfonic acid or the like, in an amount between about 5 and about 10 g%.

An alternative method of making the acid modified Carrier matrix comprises the loading of the carrier matrix with strong cation exchange resins, preferably in their Acid form. Carrier matrices loaded with ion exchange resin, which Amberlit IR 120 (Rohm & Haas, Philadelphia, Pennsylvania) or Dowex50 (Dow Chemical Co., Midland, Michigan)

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are contained as sulfonic acid-modified carrier materials particularly preferred, especially when serum is used. These special ion exchange resins are sulfonic acid modified Polystyrenes which are crosslinked with various amounts of divinylbenzene. Each support matrix will loaded with about 25 to about 50% by weight of ion exchange resin, preferably with about 35 to about 50% by weight.

Two reagents are used to prepare the test agent. One of these reagents is o-phthalaldehyde, while the other reagent is 3-hydroxy-1,2,3,4-tetrahydrobenzo / hjquinoline, 3-acetoxy-1,2,3,4-tetrahydrobenzo / h7quinoline or their dihydrochloride salts. 3-hydroxy-1,2,3,4-tetrahydrobenzo / h / quinoline is preferred.

While according to the invention, the reagents on the carrier matrix must be applied separately, the order in which the reagents are applied is not of Meaning. Any of the reagents can be applied first. The sulfonic acid material can either be simultaneous be applied to the carrier matrix with the first reagent or it can be loaded with ion exchange resin Carrier matrix can be used.

According to a preferred embodiment, the first stage comprises applying at least one reagent to the Carrier matrix. The second stage usually comprises the application of a polymer to the carrier matrix, the Polymers is in a solvent that does not dissolve the first reagent or the sulfonic acid material. Suitable polymers are e.g. methyl cellulose, cellulose acetate,

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Polyethylene oxide, styrene-butadiene copolymer, styrene-isoprene copolymer, Polystyrene and styrene-acrylonitrile copolymers. Finally, the third or last stage includes application of the other reagent on the carrier matrix, wherein the reagent is present in a solvent which is the in The polymer material applied in the second stage does not dissolve. Usually you leave the reagent strip between dry in the individual stages.

Suitable solvents for use with o-phthalaldehyde include water, methanol, acetone and hexane. Water, methanol or a mixture thereof are the preferred solvent when the reagent is o-phthalaldehyde in the first stage is applied. Acetone or hexane are the preferred solvents when the reagent is o-phthalaldehyde is applied in the third stage. With regard to the polymers, suitable solvents are: Chloroform, acetone, benzene, toluene and the like. Suitable solvents for the other reagent include water, Methanol and methanol and acetone mixtures. Again, water is the preferred solvent when using the reagent is applied in the first stage; if the reagent is applied in the third stage, either methanol is used or a methanol-acetone mixture is the preferred solvent.

The reagents can be used in various concentrations. As a rule, o-phthalaldehyde is found in an amount of about 300 mg% to 800 mg% and preferably in an amount between about 500 mg% and 600 mg%. That other reagent is usually in an amount between

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approx. 200 mg% and approx. 500 mg% before if a dihydrochloride salt is used, and in an amount of about 600 mg% to about 1200 mg% when the free base is used. the Concentrations of the polymeric material are not critical provided that an amount between 0.5 g% and approx. 5 g% is used. Preferably the polymer Material is present in an amount between about 1 g% and 3 g%. · ..

While according to a preferred embodiment according to the Invention, the production of the test agent by a three-stage impregnation, each of which involves drying then takes place, the test agent according to the invention can also be produced by other suitable methods such as by printing on one or more sides of a matrix or by appropriate application of the separate reagents on opposite sides of a substrate or matrix.

The test agent according to the invention becomes more advantageous Used by briefly dipping a test sample or by otherwise applying a test sample to the support matrix is applied, a resulting detectable color change being observed or evaluated.

Example I.

The preparation of a test agent in the form of a test device is described below. One with hydrochloric acid (10 to 20%) pre-washed cation exchange filter paper

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ORIGINAL INSPECTED

SA-2 / which was obtained from Reeve Angel, Clifton, New Jersey and that has an exchange capacity of about 4 milliequivalents per gram of dry resin impregnated in three stages with the following solutions after washing it with deionized water and drying it became. SAZ paper contains Amberlite IR 120 ion exchange resin, which is sulfonated, whereby it gets the ion exchange shafts. The resin is in the sodium form and the paper contains between 45 and 50% of this resin.

First impregnation stage

The filter paper was impregnated by putting it in solutions which contained the following materials in the amounts indicated.

material

water

Maleic anhydride methyl vinyl ether copolymer (stabilizer)

Boric acid (color stabilizer) o-phthalaldehyde

7- (2,3-dihydroxypropyl) -

theophylline (stabilizer) 10

After impregnation, the paper was dried at 60 ° C. for 30 minutes. ^f "" -.

lot ml 100 mg 100 G 2.5 mg 300

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Second impregnation stage

The dried, impregnated paper of the first stage was then impregnated by immersing it in a solution containing the following materials in the amounts indicated.

Material quantity

Toluene 100 ml

Polystyrene beads
(Styron, Dow Chemical Co.,
Midland, Mich.) 2 g

Third stage of impregnation

The dried, impregnated paper from the second stage was then impregnated by immersion in a solution, which contained the following materials in the amounts indicated. Materials (1) and (4) were first dissolved, materials (2) and (3) were separately dissolved and then materials (1) and (4) to form a solution admitted.

, Lot

(1) methanol 30 ml

(2) acetone 70 ml

(3) hydroxypropyl cellulose
(Stabilizer) 0.5 g

(4) S-Hydroxy-I ^ S ^ -tetrahydrobenzo ^ h / quinoline-hydro-

chloride ~ "300 mg

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The paper was then 10 minutes;

mg dried at 60 ° C and then by means of a double-sided adhesive tape Applied to a polystyrene uriter layer or a carrier. The polystyrene support ensures a suitable handle or a handle for immersing the obtained Paper test strip or the test device into a solution in order to determine the urea content of the solution.

The color intensity of the urea nitrogen reagent strips for different urea concentrations is shown in the following table.

Part of a serum sample that contains the specified amount Contains urea nitrogen, is mixed with 2 parts of water diluted and 0.030 ml is applied to the surface of the test strip prepared in Example 1. To Incubating at 37 ° C for 1 minute will increase the reflectivity of the reagent strip at 620 nm in relation to a barium sulfate, white reflection surface determined.

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BATH ORIGINAL Table 1

Urea-
nitrogen
concentration
(mg%) % Reflect
functional
strength Urea-
nitrogen
concentration
(mg%) % Reflect
functional
strength 0 75 50 30th 5 62 60 27 10 54 70 25th . 20th 44 90 21st 30th 38 120 18th 40 33 150 15th

Example II

The preparation of another test agent will now be described. A Dowex 5OW filter paper loaded with 40% by weight, which is available in acid form and 8% with divinylbenzene (Dow Chemical Co., Midland, Mich.) was impregnated in three stages with the following solutions.

First impregnation stage

The filter paper was impregnated by immersion in a solution containing the following materials in the specified Amounts contained.

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material

water

Polyethylene oxide

o-phthalaldehyde

7- (2 _f 3-dihydroxypropy1) -theophyillin (stabilizer)

Boric acid

After the impregnation, the paper was long for 30 minutes dried at 60 ° C.

lot ml 100 mg 50 mg 300 G 10 G 2.5

Second impregnation stage

The dried impregnated paper from the first stage was then impregnated by immersion in a solution containing the following materials in the specified amounts contained.

Material quantity

Toluene 100 ml

Styrene acrylonitrile

Copolymer 2g

After impregnation with the styrene copolymer, the paper was dried at 60 ° C. for 15 minutes.

Third stage of impregnation

The dried, impregnated paper from the second stage

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was then impregnated by immersion in a solution containing the following materials in the specified amounts contained. Materials (1) and (4) were first dissolved; materials (2) and (3) were separately dissolved and then added to materials (1) and (4) to form a solution.

Material quantity

(1) methanol 30 ml

(2) acetone 70 ml

(3) hydroxypropyl cellulose 0.5 g

(4) 3-Acetoxy-1,2,3,4-tetrahydrobenzo _< / E7quinoline hydrochloride 300 mg

The paper was then dried at 60 ° C. for 10 minutes and applied to a polystyrene support by means of a double-sided adhesive tape. The polystyrene support creates a suitable handle or a handle, with which the obtained, reagent-impregnated test device in a Solution is immersed to determine the urea content of the solution.

Additional test agents were prepared using the same procedure as described in Example II, using Dowex 5OW was used, which was 2% with divinylbenzene and 16% was crosslinked with divinylbenzene. It was found that the formed by immersion in a urea sample Color intensity could be controlled by varying the proportion of crosslinking. The intensity was inversely related to the degree of crosslinking.

The speed of color formation of the urea nitrogen reagent strips, which have been made with straps

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were the ion exchange resins with different Divinylbenzene (DVB) crosslinking is shown in the following table.

Reagent strips were used as in Example II of ion exchange resin loaded paper containing Dowex 50 resins with 2%, 8% and 16% divinylbenzene crosslinking contained, manufactured. The urea samples were then diluted, incubated for 1 minute at 37 ° C and evaluated on a reflectometer as in Table 1.

. Table 2

DETERMINATION OF REFLECTIVE STRENGTH FOR DIFFERENT UREA CONCENTRATIONS AND VARIOUS DVB NETWORKING (THE VALUES THE REFLECTIVE STRENGTH AND COLOR INTENSITY ARE IN THE REVERSE RATIO)

Urea-
nitrogen
concentration
(mg%) % DVB networking 2 8th 16 20th
40
60 37
27
21 44
33
27 66
56
50

The speed of color formation of the urea nitrogen reagent strips, which were made from beams that

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are loaded with varying amounts of ion exchange resin / is shown in the following table.

There were as in Example I reagent strips made of a paper loaded with ion exchange resin, which 25, 35 and % By weight of an 8% divinylbenzene crosslinked ion exchange resin contained / prepared. The urea samples were diluted / incubated for 1 minute at 37 C and measured on a reflectometer as in Table 1.

Table 3

REFLECTIVE STRENGTH READINGS FOR VARYING UREA CONCENTRATIONS AND VARIATING RESIN CONTENT

mg% urea nitrogen
concentration % Resin content 25th 35 50 20th
40
60 58
48
42 51
40
33 44
33
27

Example III

Using an ion exchange paper as described in Example II, test devices or Test strips produced according to the following 3-step process.

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First impregnation stage

The paper was impregnated by immersing it in a solution containing the following materials in the amounts indicated.

Material. lot

Water 25 ml

Polyethylene oxide 100 mg

7- (2,3-dihydroxypropyl) -

theophylline 10 g

Ethylenedinitrilotetraacetic

acid, dipotassium salt 1.5 g

Sodium Lauryl Sulphate 100 mg

Methanol 75 ml

Glycerin 0.2 ml

Boric acid 4.5g

o-phthalaldehyde 600 mg

After the impregnation, the paper was dried at 50 ° C. for 20 minutes.

Second impregnation stage

Material. lot

Toluene 100 ml

Polystyrene beads (pellets) 3g

After impregnation with the styrene polymer, the paper became Dried at 50 ° C for 10 minutes.

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ORIGINAL INSPECTED

Third stage of impregnation

The dried impregnated paper from the second stage was then impregnated by immersion in a solution, which contained the following materials in the amounts indicated. Materials (2), (3) and (4) became separate combined and then the material (1) was added to form a solution.

Material quantity

(1) methanol 25 ml

(2) acetone 75 ml

(3) hydroxypropyl cellulose 0.75 g

(4) 3-Hydroxy-1,2,3,4-tetrahydrobenzo / E7quinoline 900 mg

The paper was dried at 50 ° C for 5 minutes. The test strip obtained can be used for blood serum or plasma, which have not been diluted, as is required in the case of the test strips of Examples I and II, for Concentrations up to 70 mg% urea nitrogen can be used.

It goes without saying that the use of the stabilizer hydroxypropyl cellulose for the present invention is not critical. It should also be noted that a stabilizer, such as caffeine, instead of dyphylline, which is used in the following example can be used. It has been shown that dyphylline or its Substitute should be used in amounts above 5 g%.

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Example IV

For comparison purposes, another test strip was used after the. following procedure.

First stage

Whatman 3MM filter paper is made by dipping in a solution which contained the following materials in the specified amounts, acid-modified.

material

water
Benzene disulfonic acid

N-naphthylethylenediamine dihydrochloride

Dyphyllin '. ■

Maleic anhydride-methyl vinyl ether copolymer (stabilizer) 0.1 g

After impregnation, the paper was at for 20 minutes 60 ° C dried.

lot ml 100 G 10 mg 400 G 10

Second step

The dried impregnated paper from the first stage is then impregnated by immersion in a solution containing the following materials in the amounts indicated.

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Material quantity

Polyethylene oxide 1 g

Chloroform 70 ml

Acetone 30 ml

The paper was then dried at 60 ° C for 20 minutes.

Third step

The dried, impregnated paper from the second stage was then immersed in a solution containing the following Materials contained in the specified amounts, impregnated.

Material ^M ££ 2§

Hexane 100 ml

o-phthalaldehyde x 300 mg

The paper was then dried at 60 ° C for 20 minutes as before. The dried, impregnated paper obtained was then applied to a polystyrene support with the aid of double-sided adhesive tape. The reagent strip obtained can then be used for the quantitative determination of deproteinized samples. When trying quantitative Carrying out determinations in protein-containing samples results in undesirable precipitate formation. this fact shows in particular the great importance of the invention.

As the above shows, it is with help

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of the invention possible / all of the above To accomplish goals and possibilities, resulting in further advantages which are inherent in the system. By producing reagent strips according to the present invention The invention solves three specific problems.

First, under the usual acidic conditions of the provisions Serum proteins usually fail and interfere with the development of the chromogen. The present Invention eliminates the precipitation of serum proteins, by using a paper loaded with a strong cation exchanger a suitable acidic matrix creates.

Second, the reagents used are usually unstable. The present invention provides a method are available in which the reagents are incorporated on a paper matrix in a format such that the Reagents are stabilized.

Third, according to the present invention, the error in the reflection spectroscopic measurements to determine the urea content in the blood serum to a minimum reduced. According to the invention, a coupling agent is used which forms a chromogen that is in Wavelengths well over 550 nm can be detected. This causes the problems as a result of one on the strip occurring yellow blind reaction and the. color influence caused by bilirubin and / or turbidity in the serum, which in absorption or reflection spectroscopy

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be observed, overcome. By using 3-hydroxy-1,2,3,4-tetrahydrobenzo ^ h / quinoline or its Dihydrochloride salt becomes the blank reaction that occurs reduced to a minimum. In contrast, when using Primachin-diphosphat- ^ 8- (4-amino-imethylbutylamino) -6-methoxyquinoline / or N-naphthylethylenediamine dihydrochloride the chromogen formed has a color which at wavelengths near the absorption maximum the blind reaction must be measured. Thus, the use of 3-hydroxy 1,2,3,4-tetrahydrobenzo ^ h / quinoline allows or its dihydrochloride salt the measurement at wavelengths at which the color due to the Blind reaction is minimal.

In addition, according to the invention, all reagents incorporated into a single matrix without the use of caustic or corrosive liquid reagents.

Although according to the invention, as stated, it is particularly by determining the urea content of body fluids the invention finds it important to be able to carry out an early diagnosis of physiological disorders also an important application in the precise determination of urea in industrial wastewater, in which the urea concentration must be kept within certain limits. Means for the determination of urea containing Liquids, be it for industrial or physiological purposes, are of great importance when with Help the test agent make the determination as quickly, reliably and simply as possible, so that they can be of the Technicians can easily be learned to perform.

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It also needs in the case of medical diagnosis the test agent will be so accurate to changes in condition of a patient. All of these objects can be achieved with the aid of the invention.

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Claims (12)

HOFFMANN · EITLE "&" PAMNER ^: "''' DR. ING. E. HOFFMANN (1930-1976). DJPL.-ING. W. EITLE DR. RER. NAT. K. HOFFMANN DIPL.-ING. W. LEHN DIPL.-ING. K. FDCHSLE DR. RER. NAT. B. HANSEN ARABELLASTRASSE 4 (STERN HAUS) D-8000 MO NCHEN 81 TELEPHONE (089) 911087 TELEX 05-29-19 (PATHE) 32 167 m / wa MILES LABORATORIES. INC., ELKHART, INDIANA / USA Test agent and method for determining the urea content in liquids PATENT CLAIMS Test agent for the detection of urea, characterized in that it is one with a comprises strong cation exchange resin loaded carrier matrix, which is in the acid form, these separately from each other the reagent o-phthalaldehyde and a reagent from the group 3-hydroxy-1,2,3,4-tetrahydrobenz ^ h / quinoline, 3-acetoxy-1,2,3,4-tetrahydrobenzo ^ h / quinoline and its dihydrochloride salts incorporated therein. 2. Test agent according to claim 1, characterized in that it is 3-acetoxy ~ 1,2,3,4-tetrahydrobenzo ^ h / quinoline includes. 9098.51 / 0694 3. Test agent according to claim 1, characterized in that it is 3-hydroxy-1,2,3,4-tetrahydrobenzo ^ h7quinoline includes. 4. Test agent according to claims 2 or 3, characterized in that the reagent is o-phthalaldehyde in an amount of from about 300 mg% to about 800 mg% and the other reagent in an amount of about 200 mg% to about 500 mg% is present when the dihydrochloride salt is used, and in an amount from about 600 mg% to about 1200 mg% when the free base is used. 5. Test agent according to claim 1, characterized in that the reagents from each other be separated by a polymeric material. 6. Test agent according to claim 1, characterized in that the carrier matrix is an absorbent Represents cellulose paper matrix. 7. Test agent according to claim 6, characterized in that the carrier matrix with about 25 to about 50 weight percent ion exchange resin is loaded. 8. Test agent according to claim 7, characterized in that the ion exchange resin a resin between about 2 and about 16% divinylbenzene crosslinking represents. , 9. Method for the detection of urea in a liquid 909851/0694 "" 3 "■ Test sample, characterized in that that for a moment the test agent according to claim 1 is immersed in the test sample and the resulting detectable color change is evaluated. 10. The method according to claim 9, characterized in that the test sample is a blood serum represents. 11. The method according to claim 9, characterized in that the color change by measuring a change in the reflection strength at over about 550 nm is determined. 12. A method for the production of test agents for determining the urea content in liquids, characterized in that a carrier matrix loaded with a strong cation exchange resin, which is in its acidic form, is incorporated with first and second reagents which are separated from one another by a polymeric material , wherein the first reagent o-phthalaldehyde and the second reagent 3-hydroxy-1 , 2 , 3,4-tetrahydrobenzo / h / quinoline, 3-acetoxy-1,2,3,4-tetrahydrobenzo / h / quinoline or their dihydrochloride - includes salts. 909851/0694